MEMS have many applications including micro optical components, such as Fresnel lenses, optical gratings and corner cube reflectors. The structures are usually fabricated on a silicon substrate. Microelectronics encompass an even broader range of devices. In the field of microelectronics, micro-scale gaps are sometimes required for insulation between two materials.
Some MEMS require a microstructure, typically formed of polysilicon or nickel, to extend suspended, free standing in space, from another portion of the MEMS device. This is achieved in microfabrication by forming the microstructure around a sacrificial layer, which is later removed to release the microstructure. Conventionally, the selective release of a suspended microstructure is accomplished by a wet etch process to remove the sacrificial layer.
Wet etch release has the drawback of stiction, where the liquids used in etching cause adhesion between the suspended microstructure and other portions of the MEMS being fabricated. The stiction results from process induced capillary action. Often, the small microstructure possesses insufficient restoring forces to overcome the adhesion and the result is a useless device. Artisans have sought to overcome stiction in the wet etch process. Techniques have been developed with the use of diffusion etch holes and without, but such techniques slow the etch process and still suffer problems, though reduced, from stiction.
Hui et al, developed a dry release process described in "Carbonized Parylene as a Conformal Sacrificial Layer", Proceedings from the Solid State Sensor and Actuator Workshop, Hilton Head Island, S.C., Jun. 6-11, 1998. This technique, being a dry release, avoids problems of stiction altogether. However, this technique embodies careful handling requirements and a limited process window. Specifically, the technique requires deposition of an adhesion layer, a flow prevention hardening step in a CHF.sub.3 and He plasma, a pre-bake in N.sub.3, a carbonization step at 700.degree. C.-1000.degree. C. for an hour, and an oxidation step at 700.degree. C. for an hour.
Accordingly, there is a need for an improved suspended microstructure release process which addresses some or all of the aforementioned problems. Applications requiring micro-scale gaps similar to those between a suspended microstructure and an opposing surface would similarly benefit from such a process. These needs are met by the present dendritic sacrificial layer dry release micro-scale gap formation method.